See http://developers.sun.com/solaris/developer/support/driver/docs/usbups_whitepaper.html. Need to install the ugen driver instead of the hid driver, which doesn't support ups devices.

 prtconf -v
 ...
            input, instance #4
                Driver properties:
                    name='pm-components' type=string items=3 dev=none
                        value='NAME= hid4 Power' + '0=USB D3 State' + '3=USB D0
State'
                Hardware properties:
                    name='driver-minor' type=int items=1
                        value=00000000
                    name='driver-major' type=int items=1
                        value=00000002
                    name='low-speed' type=boolean
                    name='usb-product-name' type=string items=1
                        value='Back-UPS RS 1500 FW:8.g8 .D USB FW:g8 '
                    name='usb-vendor-name' type=string items=1
                        value='American Power Conversion'
                    name='usb-serialno' type=string items=1
                        value='BB0100009999  '
                    name='usb-release' type=int items=1
                        value=00000110
                    name='usb-num-configs' type=int items=1
                        value=00000001
                    name='usb-revision-id' type=int items=1
                        value=00000106
                    name='usb-product-id' type=int items=1
                        value=00000002
                    name='usb-vendor-id' type=int items=1
                        value=0000051d
                    name='compatible' type=string items=8
                        value='usb51d,2.106' + 'usb51d,2' + 'usbif51d,class3.0.0' + 'usbif51d,class3.0' + 'usbif51d,class3' + 'usbif,class3.0.0' + 'usbif,class3.0' + 'usbif,class3'
                    name='reg' type=int items=1
                        value=00000001
                    name='assigned-address' type=int items=1
                        value=00000004
                Device Minor Nodes:
                    dev=(53,8)
                        dev_path=/pci@1f,0/usb@c,3/input@1:hid_-124_4
                            spectype=chr type=minor
                            dev_link=/dev/usb/hid2
 
 ...
lemon(tcsh)# rem_drv ugen
lemon(tcsh)# add_drv -i '"usb51d,2.106"' -m '* 0666 root sys' ugen
devfsadm: driver failed to attach: ugen
Warning: Driver (ugen) successfully added to system but failed to attach

...
prtconf -D
        usb, instance #0 (driver name: ohci)
            input, instance #0 (driver name: ugen)
            mouse, instance #1 (driver name: hid)
            keyboard, instance #3 (driver name: hid)
...
gdowdin@lemon[99] ls -l /dev/usb/51d.2/0/
total 5
lrwxrwxrwx  1 root root 57 Mar 23 14:43 cntrl0 -> ../../../../devices/pci@1f,0/usb@c,3/input@1:51d.2.cntrl0
lrwxrwxrwx  1 root root 61 Mar 23 14:43 cntrl0stat -> ../../../../devices/pci@1f,0/usb@c,3/input@1:51d.2.cntrl0stat
lrwxrwxrwx  1 root root 58 Mar 23 14:43 devstat -> ../../../../devices/pci@1f,0/usb@c,3/input@1:51d.2.devstat
lrwxrwxrwx  1 root root 57 Mar 23 14:43 if0in1 -> ../../../../devices/pci@1f,0/usb@c,3/input@1:51d.2.if0in1
lrwxrwxrwx  1 root root 61 Mar 23 14:43 if0in1stat -> ../../../../devices/pci@1f,0/usb@c,3/input@1:51d.2.if0in1stat